time base calibration

No matter how miniscule on a relative basis, a lot of material is being moved up and down on a daily basis. Something eventually has to give...

So much for the solid Earth!

Not any more than rolling at a constant speed of 160 km/h causes friction between the driver and his seat. Your average 40-ton truck passing by causes a good deal more stress to the ground than gradients of tidal forces.

I haven't yet had time to do my own calculations or even think much abuot the quantitative arguments presented here, so I apologize for that. But this point you make doesn't seem to mention the fact that we already know, a priori, the approximate period involved here and can use that knowledge to exclude "fast" signals like an earthmover or explosion. An analysis also involves what amounts to averaging, not differentiation, so that works in the favor of being able to make a detection consistently, I suspect.

Jon

Google gave me about a 1/4 million hits on "tide effects on pendulum".

First hit concludes,

" In summary, the 9.8 m/s² value for g changes in the 2nd or 3rd decimal place from location to location and changes in the 6th decimal place from hour to hour. The temporal variations are bounded and predictable; they average down over time, but never quite to zero. These "ripples" in g cause variations in pendulum clock rate on the order of 1×10-7, which is equivalent to milliseconds per day. "

I would think this could be measured with modest equipment. but would still require a clock stability in the order of 1 part in 10-8. Lots of samples over a few months should be able to filter out effects of sun and moon

w..

J> >

Good link.

I think this part was badly worded "changes in the 6th decimal place from hour to hour.", as that is not supported by the excellant data on the link. That shows 12hr(lunar) and 24hr(solar) period effects, both in the order of 50-100 parts per billion

The figure labeled "lunar-only component" is interesting, as it seems to be (Measured g - Solar) - there must surely be another effect still here, as I cannot see the lunar G varying quite like that !

- it could be the centre of gravity, and even the tides themselves as they are close to resonant, and phase delayed and have a 28 day cycle ? Pity that graph does not have a 28 day tme axis.

-jg

I did a double take on that as well. I agree badly worded but since g is about 10 the 6th decimal point is about 1 part in 10-7. that is the right order of magnitude for 100 x 10-9 so it is obfuscated but correct.

I agree

As a small side note an old family friend used to show up for parties as a full functioning physicist once the Scotch level was high enough, his early days were spent in the Antarctica, at one of these parties he described an observation technique to measure g that they used. They had a pendulum driven clock in effect a counter and a pointed a theodolit vertical using the cross hairs mark the passing of same star in 24 hour intervals. g was computed from the pendulum length and count.

This is a way off topic but he was a colorful character.

w..

Erm, you've lost track of the dicsussion, I think. Everett and I were talking about the physical effects of tidal forces on the ground itself, particularly whether they should be causing earthquakes. We weren't talking about signal analysis.

It's neither, really. Analysing these kinds of signals deals with small periodic changes in big numbers. Averaging would iron out the changes. It's a frequency analysis, basically, i.e. an averaged differentiation, sort of.

You should be able to backtrack and correlate earthquake data. It may be enough to look at earthquake and moon phase. New moons are when the earth moon add up and full moon where they subtract. It might be interesting to look at earth quakes just after the new moon like the 5.3 in Hawaii this morning. (The implication is it might take a couple tidal cycles to put an earthquake in motion) The new moon on the weekend started somewhere over the Pacific when the moon crossed the Earth moon path.

w..

It is the same force that affects the rocks as well as the water. The water integrates the movement over time and area together with some fluid dynamics. Why would the rock be static ?

Rene